From the Ground Up: Heptacodium: a multi-season knockout in the garden

About a week ago, right on schedule, the heptacodium miconioides in Sharon Richardson’s garden started blooming. Richardson invited me over to her Charlestown Township property to see it.

This all started back in May, when I wrote about some of the fragrant trees and shrubs that can bring a fourth dimension—that of fragrance—into the yard and garden. The same day that the column appeared (May 24), Richardson sent me an email. “I smiled when I read the plants you referenced in today’s article. I have both in my garden.” (H. miconioides, and Calycanthus floridus).

“If you would like to come over to see the heptacodium miconioides in the spring and/or fall, you’re welcome to do so.” I did go for a spring visit, and returned this past week to see the plant in bloom.

Imported from its native China, Heptacodium, also known as “Seven Sons plant,” is related to honeysuckle, and is the sole member of the genus Heptacodium. The “large shrub or small tree” is a surprisingly fast grower, easily achieving a height of 10 feet or more in just five years; excellent if you have a bare spot in the landscape that you want to fill in quickly.

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Several things about this plant surprised me when I encountered it in Richardson’s garden. First, the clusters of small white flowers are beautiful, and quite striking against the dark green foliage. Second, although the flowers are hailed for their fragrance, I found the aroma understated and not particularly pleasant (though not unpleasant). Third, since Heptacodium is not a native plant I was not prepared for the number of pollinators feeding on the nectar. I saw Black Swallowtail and Red Admiral butterflies, and the tree was humming with what looked like honeybees.

On this third point I discovered a sizable gap in my understanding of pollinators and host plants. Somehow, I thought that only native plants provided food for our native pollinators.

In my reading over the years, I found plenty of references to native species being the most desirable and attractive to native pollinators, but nothing about non-native plants in that role. I think that what’s possibly at work here is that the adults of some native pollinators can feed on the nectar of non-native plants, but that the host-specific plants for the larval stage (caterpillars) are native species.

Most butterfly species are limited to one or several closely-related plant species that can serve as host plants for the caterpillars.

Native insects aside, there is so much to recommend Heptacodium. It tolerates a wide variety of soils and can tolerate both sun and partial shade. It grows quickly and needs little care. It has no apparent pest/disease vulnerability.

It also blooms at the most unlikely time—the end of the season, and up to a full month, from September into October. And the show continues; after the blossoms drop, stunning cherry-red, flower-like sepals come into view.

On the down side, this is a plant that can grow to a very large size; maximum dimensions are in the range of 20 feet tall and 15 feet wide. Better to think of it as a shrubby, multi-stemmed tree rather than as a large shrub. It also can develop a leggy, somewhat ungainly form. Pruning the plant when it is young will help create a dense, more attractive habit. Limbing up the lower branches will expose the exfoliating bark, which can be attractive in itself, especially in the fall and winter landscape, when the leaves have dropped.